The present invention relates to an electromagnetic device such as for example an electromagnetic brake, an electromagnetic coupling and the like, provided with means for reducing a residual magnetism in respective parts of the device.
It is known to provide an electromagnetic brake or coupling which has a magnet housing with inner and outer pole rings, an electromagnets between the rings, and an axially movable armature disc.
In the case of a brake, the armature disc is attracted upon switching on of the electromagnet, to an end surface of the housing, which preferably is provided with a friction coating. In the case of a coupling, the armature disc is attracted to an end surface of a rotor, which is preferably provided with a friction coating. Electromagnetic brakes or electromagnetic couplings of this type are known in the art. The permanent magnetism reducing means is formed as small gaps provided in respective parts of the electromagnetic device and extending perpendicularly to the magnetic flux. Since these gaps reduce the residual magnetism, a reliable and fast release of the armature disc after switching off of the electromagnet is achieved. Therefore, shorter switching times can be obtained in the respective electromagnetic devices.
In the known electromagnetic devices the gaps for the above-mentioned purpose are formed so that in the region of the magnet housing and/or the armature disc, multi-part constructions are provided. For example, the inner pole ring or the outer pole ring of the magnet housing is axially subdivided into a plurality of parts which are then connected with one another with provision of a respective gap. It is also known to provide a recess in the region of the armature disc, in which a separate ring is inserted with interposition of a foil and connected with the remaining part of the armature disc. For example, the Japanese patent No. 5985931 discloses a two-part armature with one air gap between its two parts. The multi-part constructions are considerably expensive, especially in view of the manufacturing costs.